1. Technical Field
The present disclosure relates to a catalyst composition, and more particularly, to a catalyst composition for preparing ortho-phenylphenol (OPP).
2. Description of Related Art
OPP is a chemical product having a wide range of applications. In addition to being used as a preservative for fruits and vegetables, OPP also can be used for the synthesis of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as an intermediate of a phosphorus-based flame retardant, the synthesis of sodium ortho-phenylphenol (SOPP) as a preservative, a bactericide or a dyeing carrier, and the synthesis of ortho-phenyl phenoxy ethyl acrylate (OPPEA) as an optical material. Further, OPP can be used in other fields, such as the fields of heat stabilizers and surfactants.
There are many methods for synthesizing OPP, which can mainly be categorized into methods of either separation or synthesis. Methods of separation each includes steps of producing phenol by sulfonation of chlorobenzene, and separating and purifying the distillation residue to obtain OPP. However, with the gradual change in the method for producing phenol, such separation method is inappropriate at present due to the stringent reaction conditions and the limited yield.
Therefore, the synthesis methods are commonly used for producing OPP, and they can be further categorized into methods of sulfonation (halogenation) and hydrolysis of phenylbenzene, methods of coupling of chlorobenzene and phenol, and the like, based on the raw materials used. Currently, in terms of availability and cost consideration, cyclohexanone is widely used as a raw material in industry. In such process, cyclohexanone is first condensed to produce a dimer (2-(1-cyclohexenyl) cyclohexanone or 2-cyclohexylidene cyclohexanone). Subsequently, a dehydrogenation reaction of such dimer is performed, and thereby obtaining the product OPP. This reaction is shown by the following formula (I):

In the reaction for preparing OPP from the cyclohexanone dimer, the catalysts used can be broadly categorized into metal alloy catalysts, supported non-noble metal catalysts, and supported noble metal catalysts. Among these, as compared to the other kinds, the metal alloy catalysts are prone to cementation during the reaction, and its selectivity of the product OPP is lower, as well as stability is poorer. Moreover, the process for synthesizing a metal alloy catalyst is more complicated. For example, as shown in U.S. Pat. No. 3,932,536A, which employs a nickel-copper-aluminum-chromium alloy catalyst, the selectivity of OPP was initially 81%, and reduced to 70% after 1,000 hours of reaction.
Further, aluminum oxide, activated carbon, silicon dioxide or other metal oxides, as a single molecule or a complex, is commonly used as a carrier for the supported catalyst. A non-noble metal catalyst does not contain a noble metal as an active component, such that it is conductive to effective cost reduction. However, even though the conversion rate and the yield are not changed after such supported non-noble metal catalyst is reacted for 300 hours, the catalytic activity and the reactivity of the supported non-noble metal catalyst are still unable to meet the standard of industrial production.
It is obvious that such metal alloy catalyst and supported non-noble metal catalyst have disadvantages of the insufficient service life of the catalyst, the catalytic activity, and reactivity for industrial production.
Platinum and palladium are often used as active components for a noble metal catalyst. Such kind of catalyst is first applied in the production of OPP. For example, in CN1371897A, which employs a molecular sieve catalyst containing palladium, even though the conversion rate of a dimer was initially 98% and the selectivity of OPP was initially 100%, the conversion rate of the dimer was reduced to 92% and the selectivity of OPP was reduced to 97% after 200 hours of reaction.
In addition, for increasing the catalytic activity, other catalytic promoters are added for modifying a catalyst. As shown in Journal of China University of Petroleum (Edition of Natural Science), 2012, 36(3):165-174, it is found that, by using a catalyst in which platinum is carried by aluminum oxide and adding an appropriate amount of potassium carbonate as a catalytic promoter at an appropriate time, the selectivity could be effectively increased to 94%. However, as shown in Chemical Industry and Engineering Progress, 2004, 23(1):59-61, which relates to the use of γ-aluminum oxide carrying 0.3% by weight of platinum thereon and the addition of potassium sulfate as a catalytic promoter, even though the conversion rate of a dimer was initially 98.7% and the selectivity of OPP was initially 96.8%, the conversion rate was reduced to 88.1% and the yield of OPP was reduced to 84% after 50 hours of reaction; and the conversion rate as reduced to 88.1% and the yield of OPP was reduced to below 80% after 100 hours of reaction. Moreover, as shown in JP51-149248, which employs a catalyst in which platinum, iridium (group VIIIB) and an alkali metal hydroxide are carried by a carrier, wherein the amount of platinum is 0.1 to 5.0% by weight, the weight ratio of iridium to platinum is 0.1 to 0.4, the amount of alkali metal hydroxide is 0.5 to 8.0% by weight, and the carrier is an aluminum oxide-silicon dioxide complex carrier containing up to 0.1% iron or 90% by weight of aluminum oxide (based on the total weight of ferric oxide in the carrier). However, in such catalyst, the conversion rate of a dimer was only 92%, and the selectivity of OPP was 93%.
Besides, CN101524643 employs aluminum oxide as a carrier, platinum as an active metal, and citric acid as a competitive adsorbent, and adds sodium sulfate as a catalytic promoter for preparing a catalyst. Even though the conversion rate was initially 100% and the selectivity was initially 95%, the conversion rate was reduced to 99.8% after 2,000 hours of reaction.
From the above, although the supported noble metal catalyst exhibits higher conversion rate and selectivity, its service life is insufficient to withstand a long period of reaction. As a result, the catalytic activity cannot be effectively maintained, and the stability of the catalyst is poor.
Therefore, the most urgent problem to be solved is to increase the overall stability and the service life of catalyst.